Single-mode selection and axial mode control in a free-electron maser oscillator using a prebunched electron beam

Abstract

The effects of electron-beam prebunching on the radiation buildup process in a free-electron maser oscillator operating in the frequency range of 4-5 GHz were studied. An electron beam of 10 keV, 1 A was prebunched by means of a microwave tube section, accelerated to 70 keV, transported through a drift region by a solenoidal magnetic field and injected into a linearly polarized wiggler in which a free-electron laser interaction takes place. Single-frequency selection and locking due to electron-beam prebunching was demonstrated; we show that by tuning the electron-beam prebunching frequency we can set the oscillator frequency at any of the resonant frequencies of the cavity within the net gain bandwidth. An appreciable speedup of the oscillation buildup due to prebunching was also observed; the buildup time of radiation in the presence of prebunching is shortened compared to the case of the free-running oscillator. ͓S1063-651X͑96͒00609-5͔

Using a polarized maser to detect high-frequency relic gravitational waves

“…This can be achieved by using a linearly polarized maser beam. Maser beams in the GHz band have been generated under laboratory conditions [20,21]. In our setup of the detector, we make use of a maser beam with transverse electric mode (TEM 00 ), whose strength has a Gaussian-type distribution [35]:…”

“…For concreteness, we adopt the following parameters of the detector that can be realized in the laboratory: 5) ν e ≃ 4.5 GHz, the frequency of the maser beam in the microwave band [20,21].…”

“…The maser beam can be chosen to a free electron maser [20,21] with a great output power ∼ 2 kW, whose frequency ∼ 4.5 GHz is the one that the fractal membrane operates effectively [22,23,24]. In the presence of GWs, the background EM fields will be perturbed, giving rise to additional photon fluxes in various directions.…”

“…There is another method of detection for high frequency gravitational waves (HFGWs), which employs a a maser beam passing through a strong static magnetic field [15,16,17], and uses a microwave receiver in combination with a fractal membrane [18,19]. The maser beam can be chosen to a free electron maser [20,21] with a great output power ∼ 2 kW, whose frequency ∼ 4.5 GHz is the one that the fractal membrane operates effectively [22,23,24]. In the presence of GWs, the background EM fields will be perturbed, giving rise to additional photon fluxes in various directions.…”

Lasing and radiation-mode dynamics in a Van de Graaff accelerator–free-electron laser with an internal cavity

“…Two long magnets were used, one on each side of the wiggler to focus the e-beam in the lateral ͑wiggling͒ plane by means of a lateral magnetic-field gradient, which they produce on the wiggler axis. 12 The rf resonator utilizes curved parallel plates as a waveguide structure and has two quasioptical Talbot effect reflectors ͑wave splitters͒, one at each resonator end, which enable e-beam passage into and out of the resonator. 7,13 This type of resonator is characterized by very small Ohmic and radiation losses of about 8%, as determined by loss measurements 13 prior to the installation of the resonator in the HV terminal.…”